MONTPELIER — The state is reaping the benefit of national clean air policies that over the last generation have helped create clearer skies and led to zero days considered unhealthy over the last two years, officials said.

The Environmental Protection Agency this week reported Vermont hasn’t had what it defines as an unhealthy air quality day — when ozone levels exceed federal standards — in 2012 or 2013.

The EPA says that ozone levels are unhealthy when average concentrations exceed 0.075 parts per million over an eight-hour period. Ground level ozone is formed when pollutants react in the presence of sunlight.

Rich Poirot, Vermont’s air quality planning chief, said the last such measurement in Vermont was in Bennington on July 20, 2011, when the ozone level was measured at 0.082.

Poirot said the air quality in Vermont and the region has been improving for years, largely as the result of policies that have reduced the emission of pollutants from Midwestern power plants, a greater reliance on natural gas for power and cleaner cars.

In addition to the decreasing levels of ozone, the levels of small particles in the air, which reduce visibility, have also been decreasing.

“Whether people can perceive that is another question,” said Poirot, who has been helping keep track of air pollution in Vermont for more than 30 years.

Dave Whitcomb, who manages private plane operations at the Morrisville-Stowe State Airport, said he has noticed that the air is clearer but hadn’t connected it to improved air quality.

“Even on those hot hazy days, the visibility is not as bad as I remember those super-hot hazy days of 20 years ago,” said Whitcomb, who has worked at the airport for 27 years. “There were times when we’d take off and we couldn’t even see the surrounding mountains on a hot hazy day. I don’t remember it being like that now for several years.”

Poirot said ozone health and environmental effects are still a concern, even if the state remains below EPA levels.